1. Field of the Invention
The present invention relates to a sheet-feeding device for feeding sheets such as cut paper, and an image forming apparatus provided with the sheet-feeding device.
2. Description of the Related Art
In typical image forming apparatuses such as a copying machine, a printer, and the like, a sheet-feeding device is necessary for feeding sheets such as cut paper. In many of sheet-feeding devices provided in image forming apparatuses, a large number of sheets to be printed are stocked in advance in a sheet-accommodating section such as a sheet-feeding cassette and a sheet-feeding tray, and the sheets stacked in the sheet-accommodating section are separated and fed one after another from an uppermost layer of the sheets. Such sheet-feeding device is adopted in a sheet-feeding section of a cassette type, a manual sheet-feeding section, a document feeding section, and the like, each of which is provided in an image forming apparatus.
In some cases, a sheet-accommodating section, such as a sheet-feeding cassette and a sheet-feeding tray, provided in a sheet-feeding device includes a sheet-restricting plate. The sheet-restricting plate is movable along a rail provided on a bottom surface of a sheet-feeding cassette and comes in contact with a side surface of a sheet stack provided in the sheet-feeding cassette, so that positions of the sheets are set. Accordingly, the sheets do not move from predetermined positions, so that a stable sheet-feeding can be performed.
Further, a sheet-feeding cassette and a sheet-feeding tray are generally provided in its periphery with side walls which extend vertically upward at such positions as to surround the accommodated sheets. An example of such sheet-feeding device is described in Japanese Patent Unexamined Publication No. 2001-213528 (Page 4, FIG. 6).
The sheet-feeding cassette disclosed in the patent document mentioned above is provided with side walls having a height which is higher than a height of an uppermost layer of a sheet stack full of sheets, in other words, a sheet stack including a maximum number of sheets which can be accommodated in the sheet-feeding cassette. However, according to this configuration, when the sheet-feeding cassette is accommodated into the accommodating section, the side walls in periphery of the sheet-feeding cassette may come in contact with a slide mechanism, which is adapted to allow the sheet-feeding cassette to be freely drawn out from and accommodated into the cassette accommodating section, a sheet-feeding roller, which is adapted to send the sheets from the sheet-feeding cassette to outside, and the like, so that it becomes likely that these members are broken.
On the other hand, for the purpose of avoiding such problem as described above, a method of making a height of the side walls in periphery of the sheet-feeding cassette to be lower than a height of an uppermost layer of a sheet stack including a maximum number of sheets. For example, the height of the walls is set to be half the height of the sheet stack including a maximum number of sheets. This can reduce the above-described trouble which is caused by that the side walls in periphery of the sheet-feeding cassette come in contact with functional members provided in periphery of the cassette accommodating section when the sheet-feeding cassette is accommodated into the cassette accommodating section.
However, according to this configuration, in a case where sheets which are relatively large in size in a sheet-feeding direction are accommodated in the sheet-feeding cassette, and a user exerts a great force to accommodate the sheet-feeding cassette into the cassette accommodating section, the sheet stack tends to move with an inertia force and overcome the restriction applied by the sheet-restricting plate. Accordingly, an upstream portion of the sheets in the sheet-feeding direction may be shifted in a sheet width direction drastically. As a result, an appropriate sheet-feeding cannot be performed, so that it becomes likely that displacement of a print image due to oblique movement of the sheet or a jam may occur.